Network Working Group S. Yadav
Request for Comments: 2752 R. Yavatkar
Category: Standards Track Intel
R. Pabbati
P. Ford
T. Moore
Microsoft
S. Herzog
IPHighway
January 2000
Identity Representation for RSVP
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document describes the representation of identity information in
POLICY_DATA object [POL-EXT] for supporting policy based admission
control in RSVP. The goal of identity representation is to allow a
process on a system to securely identify the owner and the
application of the communicating process (e.g. user id) and convey
this information in RSVP messages (PATH or RESV) in a secure manner.
We describe the encoding of identities as RSVP policy element. We
describe the processing rules to generate identity policy elements
for multicast merged flows. Subsequently, we describe representations
of user identities for Kerberos and Public Key based user
authentication mechanisms. In summary we describe the use of this
identity information in an operational setting.
1. Conventions used in this document
The key Words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC-2119].
2. IntrodUCtion
RSVP [RFC2205] is a resource reservation setup protocol designed for
an integrated services Internet [RFC1633]. RSVP is used by a host to
request specific quality of service (QoS) from the network for
particular application data streams or flows. RSVP is also used by
routers to deliver QoS requests to all nodes along the path(s) of the
flows and to establish and maintain state to provide the requested
service. RSVP requests will generally result in resources being
reserved in each node along the data path. RSVP allows particular
users to oBTain preferential Access to network resources, under the
control of an admission control mechanism. Permission to make a
reservation is based both upon the availability of the requested
resources along the path of the data and upon satisfaction of policy
rules. Providing policy based admission control mechanism based on
user identity or application is one of the prime requirements.
In order to solve these problems and implement identity based policy
control it is required to identify the user and/or application making
a RSVP request.
This document proposes a mechanism for sending identification
information in the RSVP messages and enables authorization decisions
based on policy and identity.
We describe the authentication policy element (AUTH_DATA) contained
in the POLICY_DATA object. User process can generate an AUTH_DATA
policy element and gives it to RSVP process (service) on the
originating host. RSVP service inserts AUTH_DATA into the RSVP
message to identify the owner (user and/or application) making the
request for network resources. Network elements, such as routers,
authenticate request using the credentials presented in the AUTH_DATA
and admit the RSVP message based on admission policy. After a request
has been authenticated, first hop router installs the RSVP state and
forwards the new policy element returned by the Policy Decision Point
(PDP) [POL-FRAME].
3. Policy Element for Authentication Data
3.1 Policy Data Object Format
POLICY_DATA objects contain policy information and are carried by
RSVP messages. A detail description of the format of POLICY_DATA
object can be found in "RSVP Extensions for Policy Control" [POL-
EXT].
3.2 Authentication Data Policy Element
In this section, we describe a policy element (PE) called
authentication data (AUTH_DATA). AUTH_DATA policy element contains a
list of authentication attributes.
+-------------+-------------+-------------+-------------+
Length P-Type = Identity Type
+-------------+-------------+-------------+-------------+
// Authentication Attribute List //
+-------------------------------------------------------+
Length
The length of the policy element (including the Length and P-
Type) is in number of octets (MUST be a multiple of 4) and
indicates the end of the authentication attribute list.
P-Type (Identity Type)
Type of identity information contained in this Policy Element
supplied as the Policy element type (P-type). The Internet
Assigned Numbers Authority (IANA) acts as a registry for policy
element types for identity as described in the [POL-EXT].
Initially, the registry contains the following P-Types for
identity:
1 AUTH_USER Authentication scheme to identify users
2 AUTH_APP Authentication scheme to identify
applications
Authentication Attribute List
Authentication attributes contain information specific to
authentication method and type of AUTH_DATA. The policy element
provides the mechanism for grouping a collection of
authentication attributes.
3.3 Authentication Attributes
Authentication attributes MUST be encoded as a multiple of 4 octets,
attributes that are not a multiple of 4 octets long MUST be padded to
a 4-octet boundary.
+--------+--------+--------+--------+
Length A-Type SubType
+--------+--------+--------+--------+
Value ...
+--------+--------+--------+--------+
Length
The length field is two octets and indicates the actual length of
the attribute (including the Length and A-Type fields) in number
of octets. The length does not include any bytes padding to the
value field to make the attribute multiple of 4 octets long.
A-Type
Authentication attribute type (A-Type) field is one octet. IANA
acts as a registry for A-Types as described in the section 9,
IANA Considerations. Initially, the registry contains the
following A-Types:
1 POLICY_LOCATOR Unique string for locating the
admission policy (such as X.500 DN
described in [RFC1779]).
2 CREDENTIAL User credential such as Kerberos
ticket, or digital certificate.
Application credential such as
application ID.
3 DIGITAL_SIGNATURE Digital signature of the
authentication data policy element.
4 POLICY_ERROR_OBJECT Detailed information on policy
failures.
SubType
Authentication attribute sub-type field is one octet. Value of
SubType depends on A-type.
Value:
The value field contains the attribute specific information.
3.3.1 Policy Locator
POLICY_LOCATOR is used to locate the admission policy for the user
or application. Distinguished Name (DN) is unique for each User or
application hence a DN is used as policy locator.
+-------+-------+-------+-------+
Length A-Type SubType
+-------+-------+-------+-------+
OctetString ...
+-------+-------+-------+--------
Length
Length of the attribute, which MUST be >= 4.
A-Type
POLICY_LOCATOR
SubType
Following sub types for POLICY_LOCATOR are defined. IANA acts as
a registry for POLICY_LOCATOR sub types as described in the
section 9, IANA Considerations. Initially, the registry contains
the following sub types for POLICY_LOCATOR:
1 ASCII_DN OctetString contains the X.500 DN as described
in the RFC1779 as an ASCII string.
2 UNICODE_DN OctetString contains the X.500 DN described in
the RFC1779 as an UNICODE string.
3 ASCII_DN_ENCRYPT OctetString contains the encrypted X.500
DN. The Kerberos session key or digital
certificate private key is used for encryption.
For Kerberos encryption the format is the same
as returned from gss_seal [RFC1509].
4 UNICODE_DN_ENCRYPT OctetString contains the encrypted
UNICODE X.500 DN. The Kerberos session key or
digital certificate private key is used for
encryption. For Kerberos encryption the format
is the same as returned from gss_seal [RFC
1509].
OctetString
The OctetString field contains the DN.
3.3.2 Credential
CREDENTIAL indicates the credential of the user or application to be
authenticated. For Kerberos authentication method the CREDENTIAL
object contains the Kerberos session ticket. For public key based
authentication this field contains a digital certificate.
A summary of the CREDENTIAL attribute format is shown below. The
fields are transmitted from left to right.
+-------+-------+-------+-------+
Length A-Type SubType
+-------+-------+-------+-------+
OctetString ...
+-------+-------+-------+--------
Length
Length of the attribute, which MUST be >= 4.
A-Type
CREDENTIAL
SubType
IANA acts as a registry for CREDENTIAL sub types as described in
the section 9, IANA Considerations. Initially, the registry
contains the following sub types for CREDENTIAL:
1 ASCII_ID OctetString contains user or application
identification in plain ASCII text string.
2 UNICODE_ID OctetString contains user or application
identification in plain UNICODE text string.
3 KERBEROS_TKT OctetString contains Kerberos ticket.
4 X509_V3_CERT OctetString contains X.509 V3 digital
certificate [X.509].
5 PGP_CERT OctetString contains PGP digital certificate.
OctetString
The OctetString contains the user or application credential.
3.3.3 Digital Signature
The DIGITAL_SIGNATURE attribute MUST be the last attribute in the
attribute list and contains the digital signature of the AUTH_DATA
policy element. The digital signature signs all data in the
AUTH_DATA policy element up to the DIGITAL_SIGNATURE. The algorithm
used to compute the digital signature depends on the authentication
method specified by the CREDENTIAL SubType field.
A summary of DIGITAL_SIGNATURE attribute format is described below.
+-------+-------+-------+-------+
Length A-Type SubType
+-------+-------+-------+-------+
OctetString ...
+-------+-------+-------+--------
Length
Length of the attribute, which MUST be >= 4.
ti3 A-Type
DIGITAL_SIGNATURE
SubType
No sub types for DIGITAL_SIGNATURE are currently defined. This
field MUST be set to 0.
OctetString
OctetString contains the digital signature of the AUTH_DATA.
3.3.4 Policy Error Object
This attribute is used to carry any specific policy control errors
generated by a node when processing/validating an Authentication Data
Policy Element. When a RSVP policy node (local policy decision point
or remote PDP) encounters a request that fails policy control due to
its Authentication Policy Element, it SHOULD add a POLICY_ERROR_CODE
containing additional information about the reason the failure
occurred into the policy element. This will then cause an appropriate
PATH_ERROR or RESV_ERROR message to be generated with the policy
element and appropriate RSVP error code in the message, which is
returned to the request's source.
The AUTH_DATA policy element in the PATH or RSVP message SHOULD not
contain the POLICY_ERROR_OBJECT attribute. These are only inserted
into PATH_ERROR and RESV_ERROR messages when generated by policy
aware intermediate nodes.
+----------+----------+----------+----------+
Length A-Type SubType(0)
+----------+----------+----------+----------+
0 (Reserved) ErrorValue
+----------+----------+----------+----------+
OctetString ...
+----------+----------+----------+----------+
Length
Length of the attribute, which MUST be >= 8.
A-Type
POLICY_ERROR_CODE
ErrorValue
A 32-bit bit code containing the reason that the policy decision
point failed to process the policy element. Following values have
been defined.
1 ERROR_NO_MORE_INFO No information is available.
2 UNSUPPORTED_CREDENTIAL_TYPE This type of credentials is
not supported.
3 INSUFFICIENT_PRIVILEGES The credentials do not have
sufficient privilege.
4 EXPIRED_CREDENTIAL The credential has expired.
5 IDENTITY_CHANGED Identity has changed.
OctetString
The OctetString field contains information from the policy
decision point that MAY contain additional information about the
policy failure. For example, it may include a human-readable
message in the ASCII text.
4. Authentication Data Formats
Authentication attributes are grouped in a policy element to
represent the identity credentials.
4.1 Simple User Authentication
In simple user authentication method the user login ID (in plain
ASCII or UNICODE text) is encoded as CREDENTIAL attribute. A summary
of the simple user AUTH_DATA policy element is shown below.
+--------------+--------------+--------------+--------------+
Length P-type = AUTH_USER
+--------------+--------------+--------------+--------------+
Length POLICY_LOCATOR SubType
+--------------+--------------+--------------+--------------+
OctetString (User's Distinguished Name) ...
+--------------+--------------+--------------+--------------+
Length CREDENTIAL ASCII_ID
+--------------+--------------+--------------+--------------+
OctetString (User's login ID) ...
+--------------+--------------+--------------+--------------+
4.2 Kerberos User Authentication
Kerberos [RFC1510] authentication uses a trusted third party (the
Kerberos Distribution Center - KDC) to provide for authentication of
the user to a network server. It is assumed that a KDC is present and
both host and verifier of authentication information (router or PDP)
implement Kerberos authentication.
A summary of the Kerberos AUTH_DATA policy element is shown below.
+--------------+--------------+--------------+--------------+
Length P-type = AUTH_USER
+--------------+--------------+--------------+--------------+
Length POLICY_LOCATOR SubType
+--------------+--------------+--------------+--------------+
OctetString (User's Distinguished Name) ...
+--------------+--------------+--------------+--------------+
Length CREDENTIAL KERBEROS_TKT
+--------------+--------------+--------------+--------------+
OctetString (Kerberos Session Ticket) ...
+--------------+--------------+--------------+--------------+
4.2.1. Operational Setting using Kerberos Identities
An RSVP enabled host is configured to construct and insert AUTH_DATA
policy element into RSVP messages that designate use of the Kerberos
authentication method (KERBEROS_TKT). Upon RSVP session
initialization, the user application contacts the KDC to obtain a
Kerberos ticket for the next network node or its PDP. A router when
generating a RSVP message contacts the KDC to obtain a Kerberos
ticket for the next hop network node or its PDP. The identity of the
PDP or next network hop can be statically configured, learned via
DHCP or maintained in a Directory service. The Kerberos ticket is
sent to the next network node (which may be a router or host) in a
RSVP message. The KDC is used to validate the ticket and
authentication the user sending RSVP message.
4.3 Public Key based User Authentication
In public key based user authentication method digital certificate is
encoded as user credentials. The digital signature is used for
authenticating the user. A summary of the public key user AUTH_DATA
policy element is shown below.
+--------------+--------------+--------------+--------------+
Length P-type = AUTH_USER
+--------------+--------------+--------------+--------------+
Length POLICY_LOCATOR SubType
+--------------+--------------+--------------+--------------+
OctetString (User's Distinguished Name) ...
+--------------+--------------+--------------+--------------+
Length CREDENTIAL SubType
+--------------+--------------+--------------+--------------+
OctetString (User's Digital Certificate) ...
+--------------+--------------+--------------+--------------+
Length DIGITAL_SIGN. 0
+--------------+--------------+--------------+--------------+
OctetString (Digital signature) ...
+--------------+--------------+--------------+--------------+
4.3.1. Operational Setting for public key based authentication
Public key based authentication assumes following:
- RSVP service requestors have a pair of keys (private key and
public key).
- Private key is secured with the user.
- Public keys are stored in digital certificates and a trusted
party, certificate authority (CA) issues these digital
certificates.
- The verifier (PDP or router) has the ability to verify the
digital certificate.
RSVP requestor uses its private key to generate DIGITAL_SIGNATURE.
User Authenticators (router, PDP) use the user's public key (stored
in the digital certificate) to verify the signature and authenticate
the user.
4.4 Simple Application Authentication
The application authentication method encodes the application
identification such as an executable filename as plain ASCII or
UNICODE text.
+----------------+--------------+--------------+--------------+
Length P-type = AUTH_APP
+----------------+--------------+--------------+--------------+
Length POLICY_LOCATOR SubType
+----------------+--------------+--------------+--------------+
OctetString (Application Identity attributes in
the form of a Distinguished Name) ...
+----------------+--------------+--------------+--------------+
Length CREDENTIAL ASCII_ID
+----------------+--------------+--------------+--------------+
OctetString (Application Id, e.g., vic.exe)
+----------------+--------------+--------------+--------------+
5. Operation
+-----+ +-----+
PDP -------+ PDP
+-----+ ................... +-----+
: :
+--------+ : Transit : +-------+
+---- Router ------: Network : ------- Router--+
+--------+ : : +-------+
:.................:
Host A B C D
Figure 1: User and Application Authentication using AUTH_DATA PE
Network nodes (hosts/routers) generate AUTH_DATA policy elements,
contents of which are depend on the identity type used and the
authentication method used. These generally contain authentication
credentials (Kerberos ticket or digital certificate) and policy
locators (which can be the X.500 Distinguished Name of the user or
network node or application names). Network nodes generate AUTH_DATA
policy element containing the authentication identity when making the
RSVP request or forwarding a RSVP message.
Network nodes generate user AUTH_DATA policy element using the
following rules
1. For unicast sessions the user policy locator is copied from the
previous hop. The authentication credentials are for the current
network node identity.
2. For multicast messages the user policy locator is for the current
network node identity. The authentication credentials are for the
current network node.
Network nodes generate application AUTH_DATA policy element using the
following rules:
1. For unicast sessions the application AUTH_DATA is copied from the
previous hop.
2. For multicast messages the application AUTH_DATA is either the
first application AUTH_DATA in the message or chosen by the PDP.
6. Message Processing Rules
6.1 Message Generation (RSVP Host)
An RSVP message is created as specified in [RFC2205] with following
modifications.
1. RSVP message MAY contain multiple AUTH_DATA policy elements.
2. Authentication policy element (AUTH_DATA) is created and the
IdentityType field is set to indicate the identity type in the
policy element.
- DN is inserted as POLICY_LOCATOR attribute.
- Credentials such as Kerberos ticket or digital certificate are
inserted as the CREDENTIAL attribute.
3. POLICY_DATA object (containing the AUTH_DATA policy element) is
inserted in the RSVP message in appropriate place. If INTEGRITY
object is not computed for the RSVP message then an INTEGRITY
object SHOULD be computed for this POLICY_DATA object, as
described in the [POL_EXT], and SHOULD be inserted as a Policy
Data option.
6.2 Message Reception (Router)
RSVP message is processed as specified in [RFC2205] with following
modifications.
1. If router is not policy aware then it SHOULD send the RSVP message
to the PDP and wait for response. If the router is policy unaware
then it ignores the policy data objects and continues processing
the RSVP message.
2. Reject the message if the response from the PDP is negative.
3. Continue processing the RSVP message.
6.3 Authentication (Router/PDP)
1. Retrieve the AUTH_DATA policy element. Check the PE type field and
return an error if the identity type is not supported.
2. Verify user credential
- Simple authentication: e.g. Get user ID and validate it, or get
executable name and validate it.
- Kerberos: Send the Kerberos ticket to the KDC to obtain the
session key. Using the session key authenticate the user.
- Public Key: Validate the certificate that it was issued by a
trusted Certificate Authority (CA) and authenticate the user or
application by verifying the digital signature.
7. Error Signaling
If PDP fails to verify the AUTH_DATA policy element then it MUST
return policy control failure (Error Code = 02) to the PEP. The error
values are described in [RFC2205] and [POL-EXT]. Also PDP SHOULD
supply a policy data object containing an AUTH_DATA Policy Element
with A-Type=POLICY_ERROR_CODE containing more details on the Policy
Control failure (see section 3.3.4). The PEP will include this Policy
Data object in the outgoing RSVP Error message.
8. IANA Considerations
Following the policies outlined in [IANA-CONSIDERATIONS],
authentication attribute types (A-Type)in the range 0-127 are
allocated through an IETF Consensus action, A-Type values between
128-255 are reserved for Private Use and are not assigned by IANA.
Following the policies outlined in [IANA-CONSIDERATIONS],
POLICY_LOCATOR SubType values in the range 0-127 are allocated
through an IETF Consensus action, POLICY_LOCATOR SubType values
between 128-255 are reserved for Private Use and are not assigned by
IANA.
Following the policies outlined in [IANA-CONSIDERATIONS], CREDENTIAL
SubType values in the range 0-127 are allocated through an IETF
Consensus action, CREDENTIAL SubType values between 128-255 are
reserved for Private Use and are not assigned by IANA.
9. Security Considerations
The purpose of this memo is to describe a mechanism to authenticate
RSVP requests based on user identity in a secure manner. RSVP
INTEGRITY object is used to protect the policy object containing user
identity information from security (replay) attacks. Combining the
AUTH_DATA policy element and the INTEGRITY object results in a secure
access control that enforces authentication based on both the
identity of the user and the identity of the originating node.
Simple authentication does not contain credential that can be
securely authenticated and is inherently less secured.
The Kerberos authentication mechanism is reasonably well secured.
User authentication using a public key certificate is known to
provide the strongest security.
10. Acknowledgments
We would like to thank Andrew Smith, Bob Lindell and many others for
their valuable comments on this memo.
11. References
[ASCII] Coded Character Set -- 7-Bit American Standard
Code for Information Interchange, ANSI X3.4-
1986.
[IANA-CONSIDERATIONS] Alvestrand, H. and T. Narten, "Guidelines for
Writing an IANA Considerations Section in
RFCs", BCP 26, RFC2434, October 1998.
[POL-EXT] Herzog, S., "RSVP Extensions for Policy
Control", RFC2750, January 2000.
[POL-FRAME] Yavatkar, R., Pendarakis, D. and R. Guerin, "A
Framework for Policy-based Admission Control
RSVP", RFC2753, January 2000.
[RFC1510] Kohl, J. and C. Neuman, "The Kerberos Network
Authentication Service (V5)", RFC1510,
September 1993.
[RFC1704] Haller, N. and R. Atkinson, "On Internet
Authentication", RFC1704, October 1994.
[RFC1779] Killie, S., "A String Representation of
Distinguished Names", RFC1779, March 1995.
[RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S.
and S. Jamin, "Resource ReSerVation Protocol
(RSVP) - Version 1 Functional Specification",
RFC2205, September 1997.
[RFC2209] Braden, R. and L. Zhang, "Resource ReSerVation
Protocol (RSVP) - Version 1 Message Processing
Rules", RFC2209, September 1997.
[UNICODE] The Unicode Consortium, "The Unicode Standard,
Version 2.0", Addison-Wesley, Reading, MA,
1996.
[X.509] Housley, R., Ford, W., Polk, W. and D. Solo,
"Internet X.509 Public Key Infrastructure
Certificate and CRL Profile", RFC2459, January
1999.
[X.509-ITU] ITU-T (formerly CCITT) Information technology -
Open Systems Interconnection - The Directory:
Authentication Framework Recommendation X.509
ISO/IEC 9594-8
12. Author Information
Satyendra Yadav
Intel, JF3-206
2111 NE 25th Avenue
Hillsboro, OR 97124
EMail: Satyendra.Yadav@intel.com
Raj Yavatkar
Intel, JF3-206
2111 NE 25th Avenue
Hillsboro, OR 97124
EMail: Raj.Yavatkar@intel.com
Ramesh Pabbati
Microsoft
1 Microsoft Way
Redmond, WA 98054
EMail: rameshpa@microsoft.com
Peter Ford
Microsoft
1 Microsoft Way
Redmond, WA 98054
EMail: peterf@microsoft.com
Tim Moore
Microsoft
1 Microsoft Way
Redmond, WA 98054
EMail: timmoore@microsoft.com
Shai Herzog
IPHighway, Inc.
55 New York Avenue
Framingham, MA 01701
EMail: herzog@iphighway.com
13. Full Copyright Statement
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included on all such copies and derivative works. However, this
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